for questions about the usage of articles.
Articles are words that precede the substantive (a noun).
In Italian the article must agree in gender and number with the noun.
Definite articles are used to indicate that a thing is unique in some way (il/lo for masculine nouns, la for feminine nouns, i/gli for masculine nouns in plural form, le for feminine nouns in plural form).
Indefinite articles are used to indicate that a thing is not identified as unique (un/uno for masculine nouns, una for feminine nouns).